1. Field of the Invention
The present invention relates to a boat for housing semiconductor wafers, and more particularly, to a boat for semiconductor wafers for reducing the contact surface between the boat and the wafers.
2. Background of the Related Art
Generally, in semiconductor device fabrication, various processes are repeatedly carried out using primary and supplementary equipment.
A semiconductor wafer boat is used as a container for housing semiconductor wafers inside the above-mentioned semiconductor device fabrication equipment, and for loading or unloading semiconductor wafers to other fabrication equipment while housing a plurality of wafers therein.
The semiconductor wafer boat is made of a quartz material which is able to withstand the harsh fabrication environments encountered during processing, for example, a high temperature environment in a diffusion process in which an oxide layer is deposited on the wafer, or an implantation process in which boron (B) or phosphorus (P) is implanted in the wafer substrate to achieve certain electrical characteristics.
FIG. 1 shows a conventional semiconductor wafer boat which comprises: an upper member 2 and a lower member 3, between which a plurality of wafers 1 are loaded; a plurality of support members 4 for connecting the upper member 2 and the lower member 3; and a plurality of slots 5 formed in the support members 4 for supporting a wafer 1 at its peripheral edge inserted into the slots 5.
FIG. 2 shows the bottom of the wafer loaded in the boat in FIG. 1, with the areas 6 indicating the contact surface between the wafer and the boat. As shown in FIG. 2, the contact surface areas 6 have a semicircular shape.
FIG. 3 shows another conventional semiconductor wafer boat which comprises: an upper member 7 and a lower member 8 between which a plurality of wafers 1 are loaded; a plurality of support members 9 for connecting the upper member 7 and the lower member 8; and a plurality of mounting plates 10 each of which is ring-shaped for mounting a wafer 1 thereon. The wafer 1 mounted on the mounting plate 10 has a ring-shaped contact surface 11 as shown in FIG. 4.
However, a "slip" phenomenon often occurs on the wafer 1 in the conventional semiconductor wafer boats, which is caused by the contact surfaces 6 and 11 as shown in FIGS. 2 and 4. This "slip" results when fine scratches generated at the contact surface between the wafer and the boat produce crystal dislocation or cracks on the surface of the wafer.
More specifically, small vibrations often occur in the boat. Contact friction between the wafer 1 and its contacting slot 6 or mounting plate 11, having different thermal expansion coefficients, causes fine scratches on the surface of the wafer, which leads to crystal dislocation, surface distortions or cracks in the wafer. Such crystal dislocation, surface distortions or cracks are referred to as "slip".
Other contributing factors that influence the degree or severity of "slip" include high temperature processing conditions (over about 900.degree. C.), high heating rates inside a process chamber, too narrow a gap between the slots of the boat or between the mounting plates, or excessive upward/downward speed of the boat when wafers are loaded/unloaded to and from the process chamber after one process is completed.
Accordingly, in order to reduce or prevent the "slip" phenomenon, the manufacturing processes for semiconductor wafers have been modified so as to minimize these contributing factors, thereby resulting in decreased production yield of semiconductor devices.
Furthermore, the larger the contact surface between the wafer and the boat the more fine scratches occur, and the more frequently "slip" occurs. Accordingly, a large contact surface causes serious defects on the wafer, and reduces the usable area on the wafer.